Yellow Fog Lights

IN California, I have noticed that people are having their clear OEM bulbs taken out of the fog light/driving light assemblies and replaced with yellow bulbs. The clear OEM lens remains with yellow bulb inside. I talked with some of these (20-something) guys, and from their point of view, this accomplishes two things; 1) it gives their vehicle a distinctive front look when the lights are on, and 2) they gain greater lighting efficiency in fog conditions since they believe the yellow light results in less reflection off the fog. Obviously the first reason is more important, with the second reason a rationalization, but a good rationalization always helps when you change something on your car. Besides, they are not alone in that point of view – many vehicle lighting engineers believe that yellow light is much better in fog conditions for the same reason, that is, it reflects less than a clear bulb. This change mimics the factory look of many sports cars and luxury cars from the 70’s, 80’s and early 90’s, i.e., Mercedes-Benz, Acura, Ferrari, etc., and I must say, is attractive to these eyes. Since trends like this tend to start on the West Coast and go east, you have now been given the early heads-up.

Since that time, I have been deluged with questions about yellow fog lights. Since interest in this subject seems to be high, I’m going to print the most frequently-asked questions (FAQs) that I received, along with the most frequently-given answers (FGAs?), just in case others had the same questions.

Here we go:

Q: Is it true that yellow fog lights work better than clear (white) fog lights in the fog?

A: I don’t know, although I have been told this many times over the years. I am not an automotive lighting engineer. However, a former lighting engineer from Mercedes AG told me that this is true, that yellow bulbs work better because yellow light reflects less off of fog. A month later, a current automotive lighting engineer at General Motors also concurred with this opinion. Here is another fact that they both added to their answer – a yellow bulb inside a clear lens is much more efficient from a lighting perspective than a clear bulb inside a coated yellow lens. They both said that coated lenses produce a 30-50% decrease in light output, depending on how thick the coating on the lens was applied. The ex-Mercedes engineer noted that before the mid-70’s, manufacturers generally used coated lenses for yellow fog lights (as did Mercedes), but as soon as the bulb technology improved everyone went to yellow bulbs housed in clear lens modules. It should be noted, however, that there are many engineers that insist that there is no difference in light effectiveness between clear lamps and yellow lamps in fog conditions. My personal opinion, having driven cars with both types of fog lights in heavy fog conditions (I live in San Francisco) over the years, is that the yellow lights seem more effective in the fog. Also, whether it’s because it’s a different look up front or they’re more visible in bad weather, other drivers seem to be able to see me better when I have the yellow lights on a car.

A: Important distinction here: Clear driving lights are better than yellow driving lights (more light on the road way up ahead of you). Yellow fog lights are considered by many to be better than clear fog lights (more light and less reflected glare off the fog right in front of you). If you’re a manufacturer, and you have one set of lights on your car that you advertise as combination driving/fog lights, you usually go with the clear lights, because most people don’t have a clue as to the differences, and the ones that do, all want to think of themselves as drivers that go fast, so they need driving lights, because they’re cool like that. Exceptions in the U.S. include Mercedes (for approximately 35 years, until the mid-90’s), Infiniti with their SUVs, Lexus with the LS 400 and the IS series, Acura in the early 90’s, lots of European cars not sold in the States, and some others. In Europe, the dealers tend to give a choice depending on your personal driving habits: if you usually drive at sustained speeds of 100 mph or more (say, in Germany), then you need driving lights more than you need fog lights, and you probably should get the clear bulbs. If you do not or cannot typically drive that fast (like in the U.S.) and you want as much security as possible during inclement weather conditions, then the dealers will swap the bulbs out for the yellow bulbs and you’re good to go. Personal preferences/needs are important in the decision if you’re thinking about changing out your lights.

Q: Are yellow fog lights legal in the United States?

A: Yes, as noted in the previous Q&A text, many manufacturers have yellow fog lights as original equipment on their vehicles. The NHTSA is fine with yellow fog lights; it’s when you start playing around with the color of your primary headlights that they get irritable. Just make sure you get the same wattage, amps, lumens, etc. as the OEM clear bulbs you’re replacing – you can’t have any kind of lights on your car that are too bright for other motorists, whether those are headlights, fog lights, etc.

Q: Is it hard to swap out the bulbs as opposed to just getting replacement lens covers?

A: Sometime the degree of difficulty is pretty high; sometimes it isn’t. It depends on the OEM light module assembly. I pay a mechanic to swap mine out because I am dangerous with tools in my hands. Make sure the bulbs match up in terms of technical specifications.

Q: Where do I get the yellow bulbs?

A: Hella, Bosch, PIAA, Marchal, Lucas, etc. – most of the aftermarket vehicle lighting suppliers sell yellow bulbs that match up to your OEM bulbs. Some of them sell direct off websites, but most of them only sell through their dealer network – aftermarket stores or websites, auto parts places, etc. I don’t know if this is true, but I’ve been told that a lot of General Motors parts departments will order the correct bulbs for you through their aftermarket accessories division.

Q: Do the yellow lights look pretty cool?

A: Yes, I happen to think so. And it’s a relatively cheap way to make your car look cool (and different). It’s mostly young guys making the swap here in CA, lots of import tuners and sports car drivers, but I’m starting to see older guys switch their OEM fog lights out, too, and we’re talking some pretty expensive iron – Ferrari, Mercedes AMG, lots of Porsches, BMW M6, Cadillac Escalades, etc. Bulbs don’t cost much – $30, $45 at the most. Even if you have to pay someone to swap the bulbs out, you’re probably looking at $200.00 all in.

Q: Are you one of those “Fast and Furious” guys in California?

A: No.

Q: Would this be considered “retro-cool”?

A: I have no idea.

Q: Can I buy the bulbs from you?

A: No

Those are all the questions I can answer on this subject. That’s everything I know about yellow fog lights, so I hope this answered any questions you might have had.

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Author: Brendan Moore

Brendan Moore is a Principal Consultant with Cedar Point Consulting , a management consulting practice based in the Washington, DC area. He also manages Autosavant Consulting, a separate practice within Cedar Point Consulting. where he advises businesses connected to the auto industry. Cedar Point Consulting can be found at http://www.cedarpointconsulting.com.